Technical Field
The present disclosure relates to power conversion devices, and more specifically to devices enabling to convert heat into electric power.
Discussion of the Related Art
FIG. 1 is a perspective view schematically showing an example of a device 1 enabling to convert heat into electric power. Device 1 comprises two electrodes 3 and 5 having opposite surfaces separated by a distance which is on the order of atomic dimensions, for example, on the order of a few nanometers. Here and in the following description, “opposite surfaces” means surfaces facing each other and between which no solid material is interposed. Electrodes 3 and 5 are for example made of metal or of a semiconductor material such as silicon. Electrodes 3 and 5 may further comprise, on the side of their opposite surfaces, a thin coating (respectively 4 for electrode 3 and 6 for electrode 5) of an electrically conductive material of low work function, for example a metal such as cesium, or a metal oxide such as potassium peroxide (K2O2) or a cesium oxide (Cs2O). To maintain the opposite surfaces at the desired distance, spacers 7 made of an insulating material are arranged between electrodes 3 and 5 in certain regions of device 1. The free space between the opposite surfaces of electrodes 3 and 5 and spacers 7 may be placed under vacuum or filled with an inert gas.
In operation, electrode 3, also called emitter, is heated up to a temperature TH, and electrode 5, also called collector, is maintained at a temperature TC lower than temperature TH. By thermionic barrier effect, electrons are extracted from hot electrode 3 and cross the potential barrier which separates them from cold electrode 5. The short distance separating opposite electrode surfaces makes the electron transport from electrode 3 to electrode 5 by tunnel effect easier. There thus is an electron flow between hot electrode 3 and cold electrode 5 and, when a load 9 (LOAD) is connected between electrodes 3 and 5, a current flows through the load going from cold electrode 5 (positive electrode) to hot electrode 3 (negative electrode).
Power conversion devices of this type, exploiting both thermionic emission and tunnel-effect conduction phenomena, are generally called tunnel-effect power converters, or thermionic power converters, or tunnel-effect thermionic power converters.
It would be desirable to be able to improve the performance, and especially the power conversion efficiency, of tunnel-effect converters.